<!--
Licensed to the Apache Software Foundation (ASF) under one or more
contributor license agreements.  See the NOTICE file distributed with
this work for additional information regarding copyright ownership.
The ASF licenses this file to You under the Apache License, Version 2.0
(the "License"); you may not use this file except in compliance with
the License.  You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
-->
<HTML>
<BODY>

<P>Contains the implementation of the external admin APIs from
<a href="{@docRoot}/org/apache/geode/admin/package-summary.html#package_description">org.apache.geode.admin</a>.</P>

<H2>Monitoring the "health" of GemFire</H2>

<P>The health monitoring implementation comes in two pieces.  On the
client (administrator) side there is a {@link
org.apache.geode.admin.internal.GemFireHealthImpl} object that is
responsible for configuring a {@link
org.apache.geode.distributed.internal.HealthMonitorImpl} that runs
in the member VMs.  The communication between the administration
process and the member process is accomplised via a {@link
org.apache.geode.internal.admin.GemFireVM GemFireVM} from the
"internal admin" API.  The <code>HealthMonitorImpl</code> is a thread
that periodically consults a {@link
org.apache.geode.admin.internal.GemFireHealthEvaluator} that uses
a {@link org.apache.geode.admin.internal.GemFireHealthConfigImpl}
to determine the health of a GemFire component.  Most of the health
criteria are based on {@linkplain org.apache.geode.Statistics
statistics} that are maintained by GemFire.  When the
<code>HealthMonitorImpl</code> determines that the health of a GemFire
component has changed, it alerts the administrator process via a
{@link org.apache.geode.internal.admin.HealthListener}.</P>


<P>The below diagram explains how the classes that monitor the health
of GemFire are implemented.</P>

<CENTER>
<IMG src="{@docRoot}/javadoc-images/health-classes.gif" HEIGHT="803" />
</CENTER>

</BODY>
</HTML>
